Tankless water heater sucking down the juice

hillbilly

So it's about that time of year when we start looking a lot harder at all of our power consumption (being off grid). Fairly recently I finally tracked down a mysterious and substantial nighttime load: our tankless water heater (a Paloma, mounted outside). It seems so clear and obvious now that I'm a bit embarrassed that it took me this long to figure it out: being an outside unit it evidently has some sort of heating element that turns on to keep things from freezing up. So, now that we have some cold nighttime temps it turns on (sometimes for several hours a night) which also keeps the inverter on and ends up putting about an 8amp draw (measured on the trimetric at about 24.5V) or roughly 200 watts.
I'm wondering if anyone else out there has had this problem, and or any inventive solutions to dealing with it? I don't think that I can really do too much in the way of insulation without making a fire hazard. I'm kind of stumped on this one??? ideas...?

icarus

Re: Tankless water heater sucking down the juice

A couple of ideas that you might try.

I am not real familiar with the new generation Palomas, but I suspect they have a heating element in them like the Takagis do to keep them from freezing.

What you could try, (with some control to make sure you don't freeze it up) is first, build a "dog house" around the heater so that it is not subject to wind or too much outside air. Your could insulate this so that if the heater comes on, it would keep more of that heat in the "dog house" and reduce the run time. You should also insulate the incoming and outgoing pipes to make sure that they are not subject to getting cold enough to trigger the heater. (intake and exhaust baffles in the flue and intake air would help a bit as well. The flue is easy to do since the burner is fan forced combustion so the blower would open the baffle. (FasNseal makes a Stainless baffle for demand water heaters) The intake is a bit trickier to do, you could use an atmospheric stack damper so that when the fan draws air through the burner, the drop in pressure would open the intake air. What you really are trying to achieve is to reduce or eliminate cold air from flowing through the heater when it is not being used.

Another thing you could do, is simply allow a slow trickle of water to flow through the heater so that it can't freeze. You may have to unplug/switch the heater so that it wither won't fire, or won't turn on the heater. My memory of the takagi is that the heater turns on ~40f, way above the problem zone. This will waste a bit of water, but maybe that is ok.

One other option would be to circulate some water through the heater on a by pass loop using a tiny circ pump and controller. When the temp nears freezing, it could circ a a tiny bit of water from of up stream tank through the heater to keep it from freezing. With some thought and a couple of check valves, it could circulate water when needed, but not allow circulation when you are drawing hot water.

Finally, Honeywell makes a cheap "winter watchman" T-stat that you could use to power a light bulb independent of the Paloma heater. If the Paloma defaults to heat at say 40f, you could turn off or unwire the heating element, and rely on a heat lamp to turn on at say 34f.

I'll give it some more thought, but I think the simplest is to insulate the heater via a "dog house" and eliminate the natural draft. That would solve 90% of it, and in moderate climes should be enough.

Your problem illustrates one of the problems with energy efficiency, that is unintended consequences. The standing pilot heaters burn a bit more gas on an annual basis, but the pilot prevents them from freezing, almost no matter how cold it gets. With my little PH6 Palomas, I have a thermally activated stack damper so that little air is escaping from the house when the heater isn't firing, AND no cold air can come down and infiltrate from the top, causing a potential freeze issue. In climates where the temperature seldom drops much below freezing these are not big issues, but at -40, the amount of air that can come down a 3" "B" vent stack on a cold night is considerable.

Tony

hillbilly

Re: Tankless water heater sucking down the juice

Tony, thanks for the ideas, I had figured you of all people would have had some experience with this issue. I'd been thinking of the "dog house" idea, I just wasn't really sure how much it would help. I'm thinking that I would still need to have the intake and venting would still need to be exposed? My wife thought that running water would help too, I just wasn't sure if that would keep things at a temp above the temperature sensor that kicks the heat on. I guess we would also need to manually turn the water heater OFF at night so that we can circulate water through the HOT water line (the heater is downstream of the COLD water into the house); not such a big deal.
Should be cold enough for the next few nights, I'll run some tests with and without running water to see how much of a difference that makes. If nothing else that may be a good short term solution. I'll take a closer look at what I could do with the "dog house" too, otherwise we may be looking at an indoor unit... (AAHHRRRGGG, did I mention I HATE plumbing work)
Thanks again for the tips

BB.

Re: Tankless water heater sucking down the juice

Can you build a three sided box with top that you can slide around the heater (with air inlets at bottom)? Add insulation and/or foil blanket fastened to inside of box? Basically, avoid radiative cooling (clear nights open to sky) and wind (cold winter storms) from getting access to heater?

Otherwise, the old standby of a temperature valve that opens a water drain when the temperature goes below 40F (assuming water is "less costly" than 200 watt heater). If practical, release water back into storage tank/well/etc.

And I see Tony has already hit this thread--so I will stop here for now (cold weather for me is 40F).

-Bill

hillbilly

Re: Tankless water heater sucking down the juice

Bill,
I'm not so far from you (just up the hills a bit), and as near as I can tell our unit turns on somewhere right around 40F. Unfortunately, at this time we don't have a way of reusing this water as we don't have a tank and the well is way uphill from the house. So it would basically be wasting water at this moment... IF allowing water to circulate through the system would take care of the problem, then it would be certainly worth the effort and money to put a small holding tank in so we can re-use that water. Money wise, water is the cheapest thing in our lives at this moment... but I have a feeling that wont last forever, and I hate waste both financial and otherwise.
Cheers,
HB

BB.

Re: Tankless water heater sucking down the juice

Water in winter is usually less of an issue... And freezing in summer is less of an issue... ????

-Bill

hillbilly

Re: Tankless water heater sucking down the juice

Well, water is still kind of an issue for much of the winter. For instance, we've had a good month or so of cold nighttime temps, hardly any rain whatsoever... so less of an issue yes, but still hate to waste it. I'll run some tests, as I'm still not sure if running water through the system will keep the heating off or not...
Will post when I know some more, thanks for the ideas so far guys...

BB.

Re: Tankless water heater sucking down the juice

There is always the drain back... Disables the heater and drains the water out until you turn it back on in the morning. But that sounds like a pain.

If you use propane for heating in winter... Can you install a small RV type 6 gallon water heater in the home (with exhaust stack)? Waste heat will still heat the home, and the tank can supply sink needs. Turn on the big heater for wash, shower, bath time, etc.

-Bill

icarus

Re: Tankless water heater sucking down the juice

Couple of questions,, how cold is "cold"? 20f is a lot easier to deal with than -20f.

As for plumbing. Discover the joys of PEX tubing and SHARKBITE fittings. These are genius fittings that fit PEX, copper and iron pipe all in one fitting. They install with no tools, and can be removed and re-installed without damage. They are a bit spending for a complete house plumbing, but for a simple repair/relocate etc there is nothing better!

They are code approved for service in inaccessible locations. http://www.sharkbiteplumbing.com/?gclid=COf52uOxu54CFRESawod0D-klg

Available at Home Depot/Lowes/Canadian tire etc.

But back to the issue at hand. I think the dog house idea is the winner. A plywood box with 2" styro foam, with a piece of tin for the vent to go out, and a way for combustion air enter would probably do it. If you carried the box all the way to the floor, such that the intake was at the floor, there would be little or no natural draft coming through the venting system to cool it down. (Remember, cool air settles, so if there is ANY heat in the box, it won't draw air UP). I would look at the Paloma book and see what temp the freeze protection kicks in, and see if you can override it so it only comes on at ~34f instead of 40f. 40f is silly as well as wasteful.

The Paloma manual(s) are not clear at what temp the heater turns on:

"Where the water heater may be exposed to
freezing conditions, even for a short period of
time, be sure to drain all water from the unit
as instructed above.
Exposure to freezing conditions can occur
from down draft of venting system or from
installation in areas exposed to cold air.
The water heater is equipped with a Freeze
Protection Electric Heater. As long as electricity
is supplied to the water heater, it prevents
freezing inside the water heater down to an
ambient temperature of approximately
minus 20°F (-28°C) (without wind conditions).
This device only protects the internal
components of the water heater. It does NOT
protect piping and valves. Therefore, piping
and valves should be wrapped with insulation
material as instructed on page 24.
Another method of freeze prevention is by
running a small volume of water. Running
water will protect the water heater, piping
and valves.
Follow the steps below to ensure proper water
flow through the water heater and piping:
Turn off the switch on the remote control.
Close the gas shut-off valve.
Open the hot water faucet slightly until a
stream of approximately 1/8” (.32 cm) is
flowing. Be sure to check the flow
periodically"

Pretty wasteful, I would look to other alternatives. I also wouldn't count on your local Paloma dealer to be much help. The advice to "talk to your dealer" is usually a wast of time,,, not always, but usually.


Tony

hillbilly

Update: test 1

Ok, so the results of our first night of highly scientific test experiments are in.
First test was to shut all AC power off for a ten hour period (ten being an easy number to play with), so we turned off all power at 9PM other than a small DC fan for our composting toilet and the small amount of tare losses for the BOS components (roughly about 0.5amps total). We tried the water trickle method first, starting with simple ideas before moving to more major solutions. At 9PM we had about 34AH drawn out of our batteries, and at 7AM we had.... insert drum roll here.... a whopping 114AH drawn out :-(
So (70AH/10 hours) - 0.5amps = about 6.5amps average draw in the night just for keeping the water heater happy. I was actually not to surprised, as I didn't think that it was so much about keeping the internal plumbing itself from freezing as much as keeping all the other stuff at a certain temperature. As for disabling or re-rigging the temperature sensor to kick in at a lower level, I don't think I want to mess with that nor take the chance that it may damage the unit somehow. I do agree it's pretty wasteful, but I think I'll work more at trying to keep it warmer instead of messing around with the sensor.
On the questions:
Tony, cold here starts at about 40f and goes down below 20f only very rarely (don't snicker, I can hear you thinking "cold, that's not cold"). So perhaps it wouldn't take much in the way of the "dog house" insulation to make enough difference that it wouldn't keep heating all night long. You kind lost me on the "take it all the way to the floor", as it's an outside mounted unit. I'll go stare at the unit some and see if any nugget of brilliance finds it's way into my head on how to finish out the dog house, as I think you may have hit the best possible solution there.
Bill, we have a wood stove for heating, but we do use propane for our fridge, and stove. I may have missed the point on the idea of adding the hot water tank into the system; how would that help keep the tankless heater from drawing power at night?
Thanks again, more tests still to come I'm sure...

BB.

Re: Tankless water heater sucking down the juice

The small tank heater was suggested so you could drain the tankless water heater during cold weather and still have hot water for smaller uses... Probably not practical (other than the electric savings).

-Bill

hillbilly

Re: Tankless water heater sucking down the juice

ok, gotcha on that... yeah, don't really want to do that. As far as draining the unit, I don't think that it really holds much water inside it at all (I suppose there must be a small amount of residual water left inside the unit, but not much). One thing that is kind of funny to me is that turning on just the hot water is not enough to wake up the inverter, however the freeze protection sensor evidently is able to wake the inverter...

icarus

Re: Tankless water heater sucking down the juice

HB,

Sorry for the confusion about the floor. What I meant was, build a "doghouse" that extends down to near the ground. The idea being that cold air settles, so that there would be a column of air at the bottom of the dog house so that the whole system wouldn't set up a natural draft.

Here is what I would do. I would build a box with a hinged front, with foil faced thermax on the sids and front, and top. I would pass the flue vent through a piece of sheet metal on top. I would close the bottom of the box, cut a ~6" hole in the bottom, and attach a piece of stove pipe (or PVC pipe). At the end of this pipe, install an atmospheric damper, that swings shut with equal pressure, but opens with low pressure (when the combustion fan runs) This way, cold air can't migrate down from the top because of the exhaust damper, nor up from the bottom because of the atmospheric damper. http://www.amazon.com/dp/B002YCHDZW/ref=asc_df_B002YCHDZW977000?smid=A1KF2V3FQHNS87&tag=nextag-sports-mp01-delta-20&linkCode=asn&creative=380341&creativeASIN=B002YCHDZW

This is the closest I can find.

Tony

Plug the bottom of the damper with a cap.

hillbilly

Re: Tankless water heater sucking down the juice

Ok Tony,
That totally makes sense. I'll have to take a look at doing something like that. If we had even some of the money to afford a solar hot water system, I'd love to install that... but it's a ways down a rather long list of other expensive things that would be nice to do.
If we can't fix this issue, I think I would be tempted to just go with a small propane hot water tank and sell the tankless unit. Bill got me thinking about using the waste heat of a water tank, and while we couldn't use it for the main house, we could use it for the bathroom which needs a small space heater (propane).... hmmmm that just might actually turn out to be a break even on propane use overall.

icarus

Re: Tankless water heater sucking down the juice

Personally, I wouldn't trade out the tankless for a small tank unit. First, I don't know of a tank unit that is smaller than about 30 gallons. Second, since your climate is comparatively mild, a few minor mods to make the unit with stand a few days of 20f should be able to be solved pretty simply. The doghouse system that I envision might only have to be installed for a few weeks/months a year. Personally, I would unplug the unit, (installed in a doghouse, and put a reflector heat lamp on a t-stat to turn on ~35, and I think you would be surprised at how little it would have to run. Remember, if the heater is in a dog house, with the vent baffled shut, when you shut off the hot water, there is going to be a fair amount of heat captured in the doghouse so that it might take several hours to drop to near freezing, turning on the heat lamp. (You could also put the water heater on a timer and then a T-stat so it would essentially unplug after evening use say 8pm, and then plug back in at 7 am. If the temp dropped to ~35 it could then plug in and use it's own internal heater).

I think this is a case of thinking through the alternatives.

Tony

Currently -9C, going to -25 by the weekend, just sort of normal.

westbranch

Re: Tankless water heater sucking down the juice

just a few thoughts on this..and to add to Tonys idea...

if you build an airtight housing around the HWH, insulate it well with adequate clearances to eliminate potential ignition, a small 25 W incandescent bulb should do the trick if mounted BELOW the portion of the HWH that can freeze. the heat introduced will be absorbed by the metal and stay warm for a while... the light can be controlled to turn on at 38 F or whatever you need it to work at to stop the built in heater from activating. You could also set it to go off at , say, 41 F. so it is not on too long.
(BTW, you could also use a 12 or 24 v light instead of 110, as the HW unit does at this time, then there is no inverter draw, just DC8))

HTH

Eric

icarus

Re: Tankless water heater sucking down the juice

OR, as Eric suggests, you put put the light bulb INSIDE the intake air pipe, below the water heater, and you could then insulate the intake pipe with duct insulation. A 15 watt bulb would probably do it, and the duty cycle would be pretty short.

Tony

sawmill

Re: Tankless water heater sucking down the juice

When I installed our Rinnai tankless heater, my freeze concern was power loss in the middle of the night when the temp was low. I used two electric valves( one NO & one NC with an air vent) so if the power went off the heater would drain automatically.

Of course these valves use a small amount of electricity so would not be suitable for off grid. A simple solution would be two manual valves with an air vent ( to replace the electric ones) you would operate when freeze danger is present and turn off power to the heater so the heat elements do not turn on. If you have gravity water, allowing a trickle would be the simplest.

As Tony has said the use of Pex plumbing is easy and simple.

Bill

LucMan

Re: Tankless water heater sucking down the juice

Can you you move the unit inside the house?

icarus

Re: Tankless water heater sucking down the juice

Two things, The outdoor units are not UL listed or code approved for indoor use, mostly due to combustion air issues. Out doors you don't need to worry about 02 depletion.

One other note about PEX. PEX can handle repeated freezes without damage! As long as the freeze is more than 6" from a fitting it is warranted not to be damage. (The fittings, which are copper will burst!)

A couple of solenoid valves is a great idea, and you could wire/plumb them in front of some manual valves, so that 350 days a year you can deenrgize them, but during freeze season you can burn a bit of power. (on the other hand, the solenoids may draw as much as the heater element does,,,?)

I really don't think that HB should have a problem with freezing at the temps he experiences. If he just covers it like described it will be fine. You could also consider adding a shed around the heater that while technically would be "indoors" it isn't in livig space.

Tony

hillbilly

Re: Tankless water heater sucking down the juice

Thanks for all the advice guys! So I have a big question here that would really solidify my potential options: I have sort of been under the impression that the freeze protection was not only for the plumbing itself, but also for any sensitive electronics inside the unit. If it's just an issue of not freezing the piping inside, then that's a no brainer, I can simply flip the circuit breaker at night (this would still leave the rest of the house powered at night if we needed a light or something), if there was a real risk of freezing we could run a trickle of water. If on the other hand there was more to it than just protecting the pipes, then we need to go with more drastic measures.
Thanks again for the ideas...
HB

icarus

Re: Tankless water heater sucking down the juice

HB,

The electronics aren't going to care, especially at ~20f. The reason to be concerned about the heater freezing, is the small water courses inside the heater, and the diaphragms. Small water passages will freeze much faster than larger pipes.

I have never taken a Paloma/Rinnai/Takagi apart to see how the heater works, but I assume it is just a small resistance heater, controlled by the control board. The Paloma owners manual even suggests that you can keep a stream of water flowing to keep it from freezing.

As I have suggested, if you can keep the wind off it, and give it a little bit of protection I don't think you will have any worries.

Just to note, we have electronics that routinely go to -40 and are unaffected. Even items that state that service temps be above freezing, we have never had problems with. I think electronics don't care for heat much more than they don't care for cold. That said, I wouldn't rely on a critical system that was way beyond the stated service temp range. I would wait until the ambient temp warms up some before relying on such equipment. That said, I have always been warned about LCD devices, that they will freeze. They may freeze, but I have never had one suffer long term damage from freezing.

Tony

hillbilly

Re: Tankless water heater sucking down the juice

In that case I was probably way over concerned about this. I think we'll just flip the breaker at night (bathroom and hot water are the only loads on this circuit), and if we are concerned about freezing just run some water. I'll look into a small storage tank, and we can reuse that water for irrigation (or whatever is easiest to plumb). A fairly simple doghouse would probably further render this a non issue. Thanks for the help
HB